1. Field of the Invention
The present invention relates to an etchant, and more particularly, to an etchant for a multi-layered interconnection line consisting of molybdenum/copper/molybdenum nitride, a method for fabricating a molybdenum/copper/molybdenum nitride multi-layered interconnection line using the etchant, and a method for fabricating a thin film transistor (TFT) substrate using the etchant.
2. Description of the Related Art
A liquid crystal display (“LCD”), which is one of the most widely used flat panel displays, includes two substrates having a plurality of electrodes and a liquid crystal layer interposed therebetween. The voltages to the electrodes rearrange the liquid crystal molecules, thereby adjusting the transmitted amount of incident light. Specifically, a plurality of pixel electrodes are arranged in matrix form on one of the two substrates and a common electrode covers the entire surface of the other substrate. An image is displayed on the LCD by applying individual voltages to the respective pixel electrodes. On the substrate, a plurality of three-terminal TFTs are connected to the respective pixel electrodes through a plurality of gate lines and data lines that transmit signals to control the TFTs.
As the display area of the LCD increases, the gate lines and the data lines connected to the TFTs also grow longer, causing an increase in the resistance of the connection lines. To solve the signal delay problem resulting from the increase in the resistance, the gate lines and the data lines should be formed of a material having as low a resistivity as possible. Copper (Cu) is among the low resistivity materials that might be used in the interconnection lines of an LCD. However, copper has poor adhesion to the substrate which is made of an insulating material formed of a glass and semiconductors made of intrinsic amorphous silicon or doped amorphous silicon. Cu has poor chemical resistance to chemical substances, is easily oxidized or corroded when exposed to the etchants that are employed to pattern the Cu layer and may easily be over-etched or etched non-uniformly and may lift or peeling away from the substrate, thereby degrading the interconnection line's lateral profile. In addition, since Cu exposed to the etchant is oxidized or corroded, resistivity increases and reliability of the interconnection line is degraded. Consequently, there is a need for an etchant that improves the lateral profile of the interconnection line and maintains the adhesion of the Cu layer to the substrate during the process of patterning the Cu layer deposited on the substrate.